Re: [RFC v3] RISC-V: Promote Zaamo/Zalrsc to a when using an old binutils

["Patrick O'Neill" <patrick@rivosinc.com>]

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On Mon, Jun 17, 2024 at 5:51 PM Kito Cheng <kito.cheng@gmail.com> wrote:

> Maybe just add 'a' to riscv_combine_info and other logic to keep the
> same (e.g. keep the logic for skip_zaamo_zalrsc)?


I did consider unconditionally upgrading zaamo/zalrsc to ‘a’ (I think
that’s what you’re suggesting w/ riscv_combine_info).
That could cause issues if users are trying to compile for a zalrsc-only
chip with an old version of binutils. If we upgrade zalrsc -> ‘a’ for both
cc1 and binutils then cc1 will emit amo ops instead of their lr/sc
equivalent.
GCC would end up emitting insns that are illegal for the user-provided
-march string.

Patrick


> On Tue, Jun 18, 2024 at 8:03 AM Patrick O'Neill <patrick@rivosinc.com>
> wrote:
> >
> > Binutils 2.42 and before don't support Zaamo/Zalrsc. Promote
> Zaamo/Zalrsc to
> > 'a' in the -march string when assembling.
> >
> > This change respects Zaamo/Zalrsc when generating code.
> >
> > Testcases that check for the default isa string will fail with the old
> binutils
> > since zaamo/zalrsc aren't emitted anymore. All other Zaamo/Zalrsc
> testcases
> > pass.
> >
> > gcc/ChangeLog:
> >
> >         * common/config/riscv/riscv-common.cc
> >         (riscv_subset_list::to_string): Add toggle to promote
> Zaamo/Zalrsc
> >         extensions to 'a'.
> >         (riscv_arch_str): Ditto.
> >         (riscv_expand_arch): Ditto.
> >         (riscv_expand_arch_from_cpu): Ditto.
> >         (riscv_expand_arch_upgrade_exts): New function. Wrapper around
> >         riscv_expand_arch to preserve the function signature.
> >         (riscv_expand_arch_no_upgrade_exts): Ditto
> >         (riscv_expand_arch_from_cpu_upgrade_exts): New function. Wrapper
> around
> >         riscv_expand_arch_from_cpu to preserve the function signature.
> >         (riscv_expand_arch_from_cpu_no_upgrade_exts): Ditto.
> >         * config/riscv/riscv-protos.h (riscv_arch_str): Add toggle to
> function
> >         prototype.
> >         * config/riscv/riscv-subset.h: Ditto.
> >         * config/riscv/riscv-target-attr.cc (riscv_process_target_attr):
> >         * config/riscv/riscv.cc (riscv_emit_attribute):
> >         (riscv_declare_function_name):
> >         * config/riscv/riscv.h (riscv_expand_arch): Remove.
> >         (riscv_expand_arch_from_cpu): Ditto.
> >         (riscv_expand_arch_upgrade_exts): Add toggle wrapper functions.
> >         (riscv_expand_arch_no_upgrade_exts): Ditto.
> >         (riscv_expand_arch_from_cpu_upgrade_exts): Ditto.
> >         (riscv_expand_arch_from_cpu_no_upgrade_exts): Ditto.
> >         (EXTRA_SPEC_FUNCTIONS): Ditto.
> >         (OPTION_DEFAULT_SPECS): Use non-upgraded march string when
> invoking the
> >         compiler.
> >         (ASM_SPEC): Use upgraded march string when invoking the
> assembler.
> >
> > Signed-off-by: Patrick O'Neill <patrick@rivosinc.com>
> > ---
> > v3 ChangeLog:
> > Rebased on non-promoting patch.
> > Wrap all Zaamo/Zalrsc upgrade code in #ifndef to prevent compiler
> > warnings about unused/potentially undefined variables.
> > Silence unused parameter warning with a voidcast.
> > ---
> > RFC since I'm not sure if this upgrade behavior is more trouble than
> > it's worth - this is a pretty invasive change. Happy to iterate further
> > or just drop these changes.
> > ---
> >  gcc/common/config/riscv/riscv-common.cc | 111 +++++++++++++++++++++---
> >  gcc/config/riscv/riscv-protos.h         |   3 +-
> >  gcc/config/riscv/riscv-subset.h         |   2 +-
> >  gcc/config/riscv/riscv-target-attr.cc   |   4 +-
> >  gcc/config/riscv/riscv.cc               |   7 +-
> >  gcc/config/riscv/riscv.h                |  46 ++++++----
> >  6 files changed, 137 insertions(+), 36 deletions(-)
> >
> > diff --git a/gcc/common/config/riscv/riscv-common.cc
> b/gcc/common/config/riscv/riscv-common.cc
> > index 1dc1d9904c7..05c26f73b73 100644
> > --- a/gcc/common/config/riscv/riscv-common.cc
> > +++ b/gcc/common/config/riscv/riscv-common.cc
> > @@ -907,7 +907,7 @@ riscv_subset_list::add (const char *subset, bool
> implied_p)
> >     VERSION_P to determine append version info or not.  */
> >
> >  std::string
> > -riscv_subset_list::to_string (bool version_p) const
> > +riscv_subset_list::to_string (bool version_p, bool upgrade_exts) const
> >  {
> >    std::ostringstream oss;
> >    oss << "rv" << m_xlen;
> > @@ -916,10 +916,17 @@ riscv_subset_list::to_string (bool version_p) const
> >    riscv_subset_t *subset;
> >
> >    bool skip_zifencei = false;
> > -  bool skip_zaamo_zalrsc = false;
> >    bool skip_zicsr = false;
> >    bool i2p0 = false;
> >
> > +#ifndef HAVE_AS_MARCH_ZAAMO_ZALRSC
> > +  bool upgrade_zaamo_zalrsc = false;
> > +  bool has_a_ext = false;
> > +  bool insert_a_ext = false;
> > +  bool inserted_a_ext = false;
> > +  riscv_subset_t *a_subset;
> > +#endif
> > +
> >    /* For RISC-V ISA version 2.2 or earlier version, zicsr and zifencei
> is
> >       included in the base ISA.  */
> >    if (riscv_isa_spec == ISA_SPEC_CLASS_2P2)
> > @@ -945,8 +952,33 @@ riscv_subset_list::to_string (bool version_p) const
> >    skip_zifencei = true;
> >  #endif
> >  #ifndef HAVE_AS_MARCH_ZAAMO_ZALRSC
> > -  /* Skip since binutils 2.42 and earlier don't recognize
> zaamo/zalrsc.  */
> > -  skip_zaamo_zalrsc = true;
> > +  /* Upgrade Zaamo/Zalrsc extensions to 'a' since binutils 2.42 and
> earlier
> > +     don't recognize zaamo/zalrsc.  */
> > +  upgrade_zaamo_zalrsc = upgrade_exts;
> > +  if (upgrade_zaamo_zalrsc)
> > +    {
> > +      for (subset = m_head; subset != NULL; subset = subset->next)
> > +       {
> > +         if (subset->name == "a")
> > +           has_a_ext = true;
> > +         if (subset->name == "zaamo" || subset->name == "zalrsc")
> > +           insert_a_ext = true;
> > +       }
> > +      if (insert_a_ext && !has_a_ext)
> > +       {
> > +         unsigned int major_version = 0, minor_version = 0;
> > +         get_default_version ("a", &major_version, &minor_version);
> > +         a_subset = new riscv_subset_t ();
> > +         a_subset->name = "a";
> > +         a_subset->implied_p = false;
> > +         a_subset->major_version = major_version;
> > +         a_subset->minor_version = minor_version;
> > +       }
> > +    }
> > +#else
> > +  /* Silence unused parameter warning when HAVE_AS_MARCH_ZAAMO_ZALRSC is
> > +     set.  */
> > +  (void) upgrade_exts;
> >  #endif
> >
> >    for (subset = m_head; subset != NULL; subset = subset->next)
> > @@ -959,12 +991,29 @@ riscv_subset_list::to_string (bool version_p) const
> >           subset->name == "zicsr")
> >         continue;
> >
> > -      if (skip_zaamo_zalrsc && subset->name == "zaamo")
> > +#ifndef HAVE_AS_MARCH_ZAAMO_ZALRSC
> > +      if (upgrade_zaamo_zalrsc && subset->name == "zaamo")
> >         continue;
> >
> > -      if (skip_zaamo_zalrsc && subset->name == "zalrsc")
> > +      if (upgrade_zaamo_zalrsc && subset->name == "zalrsc")
> >         continue;
> >
> > +      if (upgrade_zaamo_zalrsc && insert_a_ext && !has_a_ext &&
> !inserted_a_ext)
> > +       {
> > +         gcc_assert (a_subset);
> > +         /* Insert `a` extension in cannonical order.  */
> > +         if (subset_cmp (a_subset->name, subset->name) > 0)
> > +           {
> > +             oss << a_subset->name;
> > +             if (version_p)
> > +               oss << a_subset->major_version
> > +                   << 'p'
> > +                   << a_subset->minor_version;
> > +             inserted_a_ext = true;
> > +           }
> > +       }
> > +#endif
> > +
> >        /* For !version_p, we only separate extension with underline for
> >          multi-letter extension.  */
> >        if (!first &&
> > @@ -984,6 +1033,14 @@ riscv_subset_list::to_string (bool version_p) const
> >              << subset->minor_version;
> >      }
> >
> > +#ifndef HAVE_AS_MARCH_ZAAMO_ZALRSC
> > +  if (upgrade_zaamo_zalrsc && insert_a_ext && !has_a_ext)
> > +    {
> > +      gcc_assert (inserted_a_ext);
> > +      free (a_subset);
> > +    }
> > +#endif
> > +
> >    return oss.str ();
> >  }
> >
> > @@ -1598,10 +1655,10 @@ riscv_subset_list::finalize ()
> >  /* Return the current arch string.  */
> >
> >  std::string
> > -riscv_arch_str (bool version_p)
> > +riscv_arch_str (bool version_p, bool upgrade_exts)
> >  {
> >    if (current_subset_list)
> > -    return current_subset_list->to_string (version_p);
> > +    return current_subset_list->to_string (version_p, upgrade_exts);
> >    else
> >      return std::string();
> >  }
> > @@ -1907,18 +1964,33 @@ riscv_handle_option (struct gcc_options *opts,
> >
> >  const char *
> >  riscv_expand_arch (int argc ATTRIBUTE_UNUSED,
> > -                  const char **argv)
> > +                  const char **argv,
> > +                  bool upgrade_exts)
> >  {
> >    gcc_assert (argc == 1);
> >    location_t loc = UNKNOWN_LOCATION;
> >    riscv_parse_arch_string (argv[0], NULL, loc);
> > -  const std::string arch = riscv_arch_str (false);
> > +  const std::string arch = riscv_arch_str (/*version_p*/ false,
> upgrade_exts);
> >    if (arch.length())
> >      return xasprintf ("-march=%s", arch.c_str());
> >    else
> >      return "";
> >  }
> >
> > +const char *
> > +riscv_expand_arch_upgrade_exts (int argc ATTRIBUTE_UNUSED,
> > +                               const char **argv)
> > +{
> > +  return riscv_expand_arch (argc, argv, /*upgrade_exts*/ true);
> > +}
> > +
> > +const char *
> > +riscv_expand_arch_no_upgrade_exts (int argc ATTRIBUTE_UNUSED,
> > +                                  const char **argv)
> > +{
> > +  return riscv_expand_arch (argc, argv, /*upgrade_exts*/ false);
> > +}
> > +
> >  /* Expand default -mtune option from -mcpu option, use default
> --with-tune value
> >     if -mcpu don't have valid value.  */
> >
> > @@ -1938,7 +2010,8 @@ riscv_default_mtune (int argc, const char **argv)
> >
> >  const char *
> >  riscv_expand_arch_from_cpu (int argc ATTRIBUTE_UNUSED,
> > -                           const char **argv)
> > +                           const char **argv,
> > +                           bool upgrade_exts)
> >  {
> >    gcc_assert (argc > 0 && argc <= 2);
> >    const char *default_arch_str = NULL;
> > @@ -1961,10 +2034,24 @@ riscv_expand_arch_from_cpu (int argc
> ATTRIBUTE_UNUSED,
> >    location_t loc = UNKNOWN_LOCATION;
> >
> >    riscv_parse_arch_string (arch_str, NULL, loc);
> > -  const std::string arch = riscv_arch_str (false);
> > +  const std::string arch = riscv_arch_str (/*version_p*/ false,
> upgrade_exts);
> >    return xasprintf ("-march=%s", arch.c_str());
> >  }
> >
> > +const char *
> > +riscv_expand_arch_from_cpu_upgrade_exts (int argc ATTRIBUTE_UNUSED,
> > +                                        const char **argv)
> > +{
> > +  return riscv_expand_arch_from_cpu (argc, argv, /*upgrade_exts*/ true);
> > +}
> > +
> > +const char *
> > +riscv_expand_arch_from_cpu_no_upgrade_exts (int argc ATTRIBUTE_UNUSED,
> > +                                           const char **argv)
> > +{
> > +  return riscv_expand_arch_from_cpu (argc, argv, /*upgrade_exts*/
> false);
> > +}
> > +
> >  /* Report error if not found suitable multilib.  */
> >  const char *
> >  riscv_multi_lib_check (int argc ATTRIBUTE_UNUSED,
> > diff --git a/gcc/config/riscv/riscv-protos.h
> b/gcc/config/riscv/riscv-protos.h
> > index d6473d0cd85..06b33c9f330 100644
> > --- a/gcc/config/riscv/riscv-protos.h
> > +++ b/gcc/config/riscv/riscv-protos.h
> > @@ -183,7 +183,8 @@ extern tree riscv_builtin_decl (unsigned int, bool);
> >  extern void riscv_init_builtins (void);
> >
> >  /* Routines implemented in riscv-common.cc.  */
> > -extern std::string riscv_arch_str (bool version_p = true);
> > +extern std::string riscv_arch_str (bool version_p = true,
> > +                                  bool upgrade_exts = false);
> >  extern void riscv_parse_arch_string (const char *, struct gcc_options
> *, location_t);
> >
> >  extern bool riscv_hard_regno_rename_ok (unsigned, unsigned);
> > diff --git a/gcc/config/riscv/riscv-subset.h
> b/gcc/config/riscv/riscv-subset.h
> > index fe7f54d8bc5..8384aab63cb 100644
> > --- a/gcc/config/riscv/riscv-subset.h
> > +++ b/gcc/config/riscv/riscv-subset.h
> > @@ -90,7 +90,7 @@ public:
> >                           int major_version = RISCV_DONT_CARE_VERSION,
> >                           int minor_version = RISCV_DONT_CARE_VERSION)
> const;
> >
> > -  std::string to_string (bool) const;
> > +  std::string to_string (bool, bool) const;
> >
> >    unsigned xlen () const {return m_xlen;};
> >
> > diff --git a/gcc/config/riscv/riscv-target-attr.cc
> b/gcc/config/riscv/riscv-target-attr.cc
> > index 19eb7b06d54..42c2b439e66 100644
> > --- a/gcc/config/riscv/riscv-target-attr.cc
> > +++ b/gcc/config/riscv/riscv-target-attr.cc
> > @@ -367,7 +367,9 @@ riscv_process_target_attr (tree fndecl, tree args,
> location_t loc,
> >    /* Add the string of the target attribute to the fndecl hash table.
> */
> >    riscv_subset_list *subset_list = attr_parser.get_riscv_subset_list ();
> >    if (subset_list)
> > -    riscv_func_target_put (fndecl, subset_list->to_string (true));
> > +    riscv_func_target_put (fndecl,
> > +                          subset_list->to_string (/*version_p*/ true,
> > +                                                  /*upgrade_exts*/
> true));
> >
> >    return true;
> >  }
> > diff --git a/gcc/config/riscv/riscv.cc b/gcc/config/riscv/riscv.cc
> > index c17141d909a..09943389986 100644
> > --- a/gcc/config/riscv/riscv.cc
> > +++ b/gcc/config/riscv/riscv.cc
> > @@ -9425,8 +9425,10 @@ riscv_sched_adjust_cost (rtx_insn *, int,
> rtx_insn *insn, int cost,
> >  static void
> >  riscv_emit_attribute ()
> >  {
> > +  /* Upgrade extensions if necessary for the assember to understand
> > +     Eg. Zalrsc -> a.  */
> >    fprintf (asm_out_file, "\t.attribute arch, \"%s\"\n",
> > -          riscv_arch_str ().c_str ());
> > +          riscv_arch_str (/*version_p*/ true, /*upgrade_exts*/
> true).c_str ());
> >
> >    fprintf (asm_out_file, "\t.attribute unaligned_access, %d\n",
> >             TARGET_STRICT_ALIGN ? 0 : 1);
> > @@ -9468,7 +9470,8 @@ riscv_declare_function_name (FILE *stream, const
> char *name, tree fndecl)
> >        std::string *target_name = riscv_func_target_get (fndecl);
> >        std::string isa = target_name != NULL
> >         ? *target_name
> > -       : riscv_cmdline_subset_list ()->to_string (true);
> > +       : riscv_cmdline_subset_list ()->to_string (/*version_p*/ true,
> > +                                                  /*upgrade_exts*/
> true);
> >        fprintf (stream, "\t.option arch, %s\n", isa.c_str ());
> >        riscv_func_target_remove_and_destory (fndecl);
> >
> > diff --git a/gcc/config/riscv/riscv.h b/gcc/config/riscv/riscv.h
> > index 57910eecd3e..55d0a842bf2 100644
> > --- a/gcc/config/riscv/riscv.h
> > +++ b/gcc/config/riscv/riscv.h
> > @@ -46,17 +46,24 @@ along with GCC; see the file COPYING3.  If not see
> >  #define RISCV_TUNE_STRING_DEFAULT "rocket"
> >  #endif
> >
> > -extern const char *riscv_expand_arch (int argc, const char **argv);
> > -extern const char *riscv_expand_arch_from_cpu (int argc, const char
> **argv);
> > +extern const char *riscv_expand_arch_upgrade_exts (int argc, const char
> **argv);
> > +extern const char *riscv_expand_arch_no_upgrade_exts (int argc,
> > +                                                     const char **argv);
> > +extern const char *riscv_expand_arch_from_cpu_upgrade_exts (int argc,
> > +                                                           const char
> **argv);
> > +extern const char *riscv_expand_arch_from_cpu_no_upgrade_exts (int argc,
> > +                                                              const
> char **argv);
> >  extern const char *riscv_default_mtune (int argc, const char **argv);
> >  extern const char *riscv_multi_lib_check (int argc, const char **argv);
> >  extern const char *riscv_arch_help (int argc, const char **argv);
> >
> > -# define EXTRA_SPEC_FUNCTIONS                                          \
> > -  { "riscv_expand_arch", riscv_expand_arch },                          \
> > -  { "riscv_expand_arch_from_cpu", riscv_expand_arch_from_cpu },
>         \
> > -  { "riscv_default_mtune", riscv_default_mtune },                      \
> > -  { "riscv_multi_lib_check", riscv_multi_lib_check },                  \
> > +# define EXTRA_SPEC_FUNCTIONS
>            \
> > +  { "riscv_expand_arch_u", riscv_expand_arch_upgrade_exts },
>           \
> > +  { "riscv_expand_arch_nu", riscv_expand_arch_no_upgrade_exts },
>           \
> > +  { "riscv_expand_arch_from_cpu_nu",
> riscv_expand_arch_from_cpu_no_upgrade_exts }, \
> > +  { "riscv_expand_arch_from_cpu_u",
> riscv_expand_arch_from_cpu_upgrade_exts },    \
> > +  { "riscv_default_mtune", riscv_default_mtune },
>            \
> > +  { "riscv_multi_lib_check", riscv_multi_lib_check },
>            \
> >    { "riscv_arch_help", riscv_arch_help },
> >
> >  /* Support for a compile-time default CPU, et cetera.  The rules are:
> > @@ -68,15 +75,15 @@ extern const char *riscv_arch_help (int argc, const
> char **argv);
> >
> >     But using default -march/-mtune value if -mcpu don't have valid
> option.  */
> >  #define OPTION_DEFAULT_SPECS \
> > -  {"tune", "%{!mtune=*:"                                               \
> > -          "  %{!mcpu=*:-mtune=%(VALUE)}"                               \
> > -          "  %{mcpu=*:-mtune=%:riscv_default_mtune(%* %(VALUE))}}" },  \
> > -  {"arch", "%{!march=*:"                                               \
> > -          "  %{!mcpu=*:-march=%(VALUE)}"                               \
> > -          "  %{mcpu=*:%:riscv_expand_arch_from_cpu(%* %(VALUE))}}" },  \
> > -  {"abi", "%{!mabi=*:-mabi=%(VALUE)}" },                               \
> > -  {"isa_spec", "%{!misa-spec=*:-misa-spec=%(VALUE)}" },
>         \
> > -  {"tls", "%{!mtls-dialect=*:-mtls-dialect=%(VALUE)}"},                \
> > +  {"tune", "%{!mtune=*:"
>  \
> > +          "  %{!mcpu=*:-mtune=%(VALUE)}"
>  \
> > +          "  %{mcpu=*:-mtune=%:riscv_default_mtune(%* %(VALUE))}}" },
>   \
> > +  {"arch", "%{!march=*:"
>  \
> > +          "  %{!mcpu=*:-march=%(VALUE)}"
>  \
> > +          "  %{mcpu=*:%:riscv_expand_arch_from_cpu_nu(%* %(VALUE))}}"
> }, \
> > +  {"abi", "%{!mabi=*:-mabi=%(VALUE)}" },
>  \
> > +  {"isa_spec", "%{!misa-spec=*:-misa-spec=%(VALUE)}" },
>           \
> > +  {"tls", "%{!mtls-dialect=*:-mtls-dialect=%(VALUE)}"},
>           \
> >
> >  #ifdef IN_LIBGCC2
> >  #undef TARGET_64BIT
> > @@ -103,7 +110,8 @@ extern const char *riscv_arch_help (int argc, const
> char **argv);
> >  #define ASM_SPEC "\
> >  %(subtarget_asm_debugging_spec) \
> >  %{" FPIE_OR_FPIC_SPEC ":-fpic} \
> > -%{march=*} \
> > +%{march=*:%:riscv_expand_arch_u(%*)} \
> > +%{!march=*:%{mcpu=*:%:riscv_expand_arch_from_cpu_u(%*)}} \
> >  %{mabi=*} \
> >  %{mno-relax} \
> >  %{mbig-endian} \
> > @@ -116,8 +124,8 @@ ASM_MISA_SPEC
> >  "%{march=help:%:riscv_arch_help()} "                           \
> >  "%{print-supported-extensions:%:riscv_arch_help()} "           \
> >  "%{-print-supported-extensions:%:riscv_arch_help()} "          \
> > -"%{march=*:%:riscv_expand_arch(%*)} "                          \
> > -"%{!march=*:%{mcpu=*:%:riscv_expand_arch_from_cpu(%*)}} "
> > +"%{march=*:%:riscv_expand_arch_nu(%*)} "                       \
> > +"%{!march=*:%{mcpu=*:%:riscv_expand_arch_from_cpu_nu(%*)}} "
> >
> >  #define TARGET_DEFAULT_CMODEL CM_MEDLOW
> >
> > --
> > 2.34.1
> >
>